The present invention relates to a dual-clutch assembly for a dual-clutch transmission, having an input shaft, a first friction clutch, a second friction clutch, a first output shaft, a second output shaft, a first piston/cylinder assembly, and a second piston/cylinder assembly; wherein input elements of the friction clutches are connected to the input shaft; wherein output elements of the friction clutches are each connected to one of the two output shafts; wherein the friction clutches can each be actuated by means of one of the piston/cylinder assemblies; and wherein each piston/cylinder assembly has a piston, which is supported so as to be axially movable in an associated cylinder. A dual-clutch assembly of this kind is known from DE102008055681A1.
Dual-clutch transmissions have a dual-clutch assembly and two transmission sections. The transmission sections are generally of countershaft construction. A gear change without an interruption in the tractive effort can be performed by overlapping actuation of the two clutches of the dual-clutch assembly. This type of dual-clutch transmission is suitable for motor vehicles, especially for passenger motor vehicles.
In dual-clutch assemblies, use is nowadays generally made of fluid-operated friction clutches, e.g. wet multiplate clutches. DE102008055681A1 shows a dual-clutch assembly in which a piston/cylinder assembly is assigned to each of the two friction clutches, which are nested radially one inside the other. A first friction clutch is arranged radially inside and a second friction clutch is arranged radially outside. Fluid is supplied to the piston/cylinder assemblies via rotary unions between a hub fixed to the housing and the hub shell, which is mounted rotatably on the hub. The piston/cylinder assemblies are fixed to the hub shell. Each piston/cylinder assembly has a piston and a cylinder, wherein the piston is mounted so as to be axially movable in the associated cylinder and the piston and cylinder surround a piston chamber in a pressure tight manner. Each piston chamber can be pressurized by means of fluid. When fluid is supplied to a piston chamber, the piston therein is pressed axially against plate packs of the associated friction clutch, and the friction clutch is closed owing to frictional engagement. The pressure in the piston chamber is 10 bar and above, while the axial contact pressure force of the pistons on the plate packs is 5 kN and above.
The disadvantage with this type of dual-clutch assembly is the fact that the high contact pressure forces of the pistons on the plate packs lead to high reaction forces on the cylinders, with the result that the cylinders are of correspondingly massive construction, something that requires installation space and gives rise to costs for materials.
As a solution, DE102006010113A1 shows a dual-clutch assembly having piston/cylinder assemblies fixed to a hub and having pistons which are mounted so as to be axially movable in the associated cylinder. On the side facing away from the piston, the cylinder is supported by means of a retaining ring of the hub fixed to the housing, in order in this way to absorb the reaction forces with minimum installation space and low costs for materials.
It has proven disadvantageous with this type of dual-clutch assembly that the sealing material of the cylinder can chafe on the retaining ring of the hub fixed to the housing and can thus wear.